1. Field of the Invention
The present invention relates to a personal watercraft (PWC) which ejects water rearward and planes on a water surface as the resulting reaction. More particularly, the present invention relates to an engine for the personal watercraft.
2. Description of the Related Art
In recent years, so-called jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The jet-propulsion watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom of a hull and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
In the jet-propulsion watercraft, a steering nozzle provided behind the outlet port of the water jet pump is swung either to the right or to the left, to change the ejection direction of the water to the right or to the left, thereby turning the watercraft to the right or to the left.
Meanwhile, some jet-propulsion personal watercraft are provided with a riding seat disposed along its longitudinal direction. In such a watercraft, an engine is disposed in an engine room such that a crankshaft extends in the longitudinal direction of the watercraft. The crankshaft projects rearwardly and its rear end is coupled to a pump shaft of a water jet pump, thereby driving the water jet pump.
When such a personal watercraft is on the water and splashed with water, it sometimes becomes necessary to expose the engine by opening an engine room cover (a riding seat in some models) for inspection or repair work. In such cases, an ignition plug, mounted on the engine head, is likely to be splashed with water. Further, in some personal watercraft, the engine room is defined under the riding seat. In such a personal watercraft, heat from the engine or an exhaust pipe acts on the bottom of the seat and, as a result, the seat is heated.
The present invention addresses the above-described condition, and an object of the present invention is to provide a personal watercraft equipped with an engine designed in such a way that, even when the engine is splashed with water, its ignition plug is protected from water splashes, and heat generated from the engine or from an exhaust pipe attached thereto will not act on a riding seat.
As a solution to the aforementioned problem, a first aspect of the invention provides a jet-propulsion watercraft comprising: a water jet pump including an outlet port, the water jet pump pressurizing and accelerating water taken in from outside of the watercraft and ejecting the water from the outlet port to propel the watercraft as a reaction of the ejecting water; a multi-cylinder engine having a crankshaft extending along the longitudinal direction of the watercraft; and an air box so disposed as to overlie a cylinder head of the engine and to cover substantially at least ignition plugs attached to the cylinder head.
In the personal watercraft so constituted, the air box overlies and covers the ignition plugs. In such an arrangement, even when water splashes toward the ignition plugs, such water splashes are blocked by the air box, thereby protecting the ignition plugs from water splashes. Further, since it is possible to extend the length of an intake pipe connecting the air box and an intake port of the engine, good inertia effects for air-intake are produced.
It is preferable that the engine of the above-described personal watercraft is a fuel injection-type engine. This results in an increase in intake pipe length as described above, and therefore provides enhanced intake inertia effects and engine power.
Also, it is preferable that the air box of the personal watercraft contain a throttle valve. With this structure, the effective length, which contributes to the intake inertia effects, can be further increased and mechanism parts of the valve are covered by the air box, thereby rendering the valve portion rustproof.
Further, it is preferable that the air box of the personal watercraft is so disposed as to overlie the cylinder head and to cover substantially the entire cylinder head. This constitution is capable of effectively preventing water splashes to the cylinder head and effectively preventing engine-radiated heat from transferring to the seat.
It is preferable that, in the personal watercraft, the air box is disposed over the cylinder head so as to deviate from the cylinder head toward an exhaust pipe disposed on an opposite side of an intake port of the engine with respect to the crankshaft and so as not to overlie the intake port and its vicinity. This facilitates the inspection of the components placed on the intake port side.
It is preferable that, in the personal watercraft, the air box has a through-hole vertically defined in the air box in such a way that the through-hole coincides with a position of the ignition plug in plan view. This facilitates the replacement and inspection of the ignition plug.
It is preferable that, in the personal watercraft, the through-hole is closed by a removable cap member provided on the top end of the through-hole. This facilitates the replacement and inspection of the ignition plug and enables the ignition plug to be protected against water splashes.
A second aspect of the invention provides a personal watercraft comprising a water jet pump including an outlet port, the water jet pump pressurizing and accelerating water taken in from outside of the watercraft and ejecting the water from the outlet port to propel the watercraft as a reaction of the ejecting water; a multi-cylinder engine having a crankshaft extending along the longitudinal direction of the watercraft; and a plurality of intake pipes so disposed as to traverse over a cylinder head of the engine.
In the personal watercraft so constituted, the intake pipes of relatively low temperature are located above the engine. Therefore, heat radiated from the engine is less likely to transfer upward. Further, in contrast to the personal watercraft of the first aspect of the invention, the personal watercraft of the second aspect can have a longer intake pipe length, thereby making it possible to provide greater intake inertia effects.
It is preferable that the air box of the personal watercraft is disposed on one side of the engine and connected to tip ends of the plurality of intake pipes and an exhaust pipe of the engine is disposed below the air box. Thereby, the heat from the exhaust pipe, which is going to transfer upward, is blocked by the air box. This therefore provides a constitution which is less affected by the heat from the engine, even when the riding seat is disposed above the engine room.
It is preferable that, in the personal watercraft, each of the intake pipes is arranged so as not to overlie an ignition plug provided on the cylinder head so that the ignition plug is accessible from above. This facilitates the inspection and replacement of the ignition plug.
It is preferable that, in the personal watercraft, the one side of the engine is an opposite side of the intake port with respect to the crankshaft. This makes it possible to extend the length of the intake pipe.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.